The invention relates to a method for checking an imprint, by which an imprint is read and from it a data code formed, and the data code is compared with a number of check data codes in a stored data set. Apart from this, the invention relates to an imprint checking device with a reader for scanning an imprint, a memory with at least one stored data set with a number of check data codes and a computational unit for the purpose of forming a data code from the imprint and for comparing the data code with at least one check data code.
In the pharmaceutical field, but also in other production areas, there is frequently a requirement for precise quality control of imprints, for example on labels which are affixed to medicines. As an example, it is essential in the clinical studies environment that certain fields on the label, such as the patient number or lot number, can be read in full, character for character, absolutely unambiguously and correctly, that is they can be read with no deviation from the original. Other label fields, for which it is possible to deduce a character from the context, are not subject to any such high quality requirement. Hence, a field containing the imprint “Store out of reach of children” is still unambiguously comprehensible in spite of the missing cross stroke on the third “e” which turns the “e” into a “c”. To protect the consumer the EU has issued a guideline, especially for the pharmaceutical industry, which defines the concept of content-based comprehensibility, and requires a proof of this comprehensibility in the quality control of label imprints.
The known method of satisfying this requirement is to check samples of the labels manually for the correctness of their contents. To do so, an operative reads the labels and attempts to find faults. As this activity is very tiring, faults are frequently overlooked. Apart from that, this approach only permits checking of a small fraction of all the labels.
Ways are also known for carrying out checks on label imprints, documents, imprints on objects and suchlike by machine and automatically. Such a check can be based on a pixel-wise comparison of the image between an original print master and the printed label. However, such methods are only reliable under some conditions, because they make no distinction between distortions which require rejection and tolerable ones. If a small limit is set for the tolerable pixel error, then too many errors will be output and a flood of usable labels will be rejected. If the pixel error limit is too large, then even small pixel errors can lead to incorrect letters, and hence to a corruption of the meaning. Thus, for example, a small pixel error can turn “Store out of reach of children” into the misunderstandable text “Score out of reach of children”, which cannot be tolerated. In the case of East Asian characters, such errors can have even more disastrous effects.
Ways are known in addition of checking imprints by means of OCR (Optical Character Recognition) methods. Here, an imprint is read and characters from the imprint are encoded as a data code comprising letters and digits, for example in UNICODE. This makes it possible to compare the print master and imprint directly, character by character. However, even such a method is not capable of checking faults for their corruption of the meaning. Thus, the fault “Pleese store out of reach of children” is acceptable, whereas “Please score out of reach of children” is misleading.